The invention relates to a method and device for controlling the operation of similar components in the electrical system of an electric or a hybrid electric vehicle to improve the life time of the components used in the system, and for optimizing system performance in real-time using the state of health information.
Electric or hybrid electric vehicles comprise an electrical system comprising a set of interacting and/or interdependent components functioning as a whole. Over time, each of the various components in a given system may degrade at different relative rates. Moreover, as some components tend to serve a more critical role than others in the overall function of the system, the degradation of a given component can uniquely impact system performance relative to degradation of the other components in the same system. For instance, a gradual degradation of an energy storage unit, such as a high voltage battery pack or a super-capacitor can cause an appreciable degradation in overall vehicle performance, while degraded electrical components, such as power electronics components or switches, may significantly reduce the vehicle's ability to start or function in some operating modes.
Electric or hybrid electric vehicles can be provided with on-board diagnostic systems for measuring variables representing the state and/or the performance of a particular component relative to predetermined values or calibrated thresholds. For instance, it is common to measure a battery output voltage and compare this value to calibrated high/low voltage thresholds. Battery voltage measurements can also be used for calculating the current state of health of the battery. An operator may be made aware of the need to repair a given component when the component is no longer functioning properly with respect to such thresholds. System function typically improves when a severely degraded component is eventually repaired. However, immediate repair is not always a convenient or desirable option.
Larger electric or hybrid electric vehicles, such as buses or trucks can comprise several identical or substantially identical components. For instance, an articulated vehicle can be provided with a traction battery for each driven axle. In a conventional hybrid electric vehicle, individually controllable driven axles are controlled to provide desired traction properties for the vehicle. During normal operation, an on-board diagnostic system can monitor the state and/or the performance of multiple individual components, alerting the operator when any one component malfunctions.
It is desirable to provide an improved method for monitoring the state and/or the performance of multiple individual components of the same type.
In the subsequent text, the term “life time” is used to denote the useful life time of a component, from the time of installation in a vehicle until such a time when an operational state requiring replacement of the component is detected. The term “remaining operating time” is mainly used to denote the useful life time of a component, from the time of installation in a vehicle until such a time when an operational state requiring repair of the component is detected. However, the “remaining operating time” can also be the life time of a component. Both terms indicate a parameter relating to a future point in time when the vehicle becomes inoperative due to component degradation or failure.
According to preferred embodiment, the invention relates to a method for controlling electrical components in a vehicle comprising multiple traction voltage systems, wherein each traction voltage system comprises at least one electrical component, and which electrical component has the same function in each traction voltage system. The vehicle can be an electric or a hybrid electric vehicle.
The method involves performing the steps of:                monitoring and registering the state of health of each electrical component over time;        predicting a predetermined parameter for each electrical component, which parameter is related to a future operating state inhibiting the use of the components;        determining a control strategy for each electrical component based on the state of health of the electrical components to balance the parameters towards a common value;        controlling the electrical components based on the determined control strategy.        
The above method steps are carried out continuously in a loop or intermittently at constant or variable intervals during operation of the vehicle. A central controller is provided for collecting sensor data from components to be monitored, for performing required calculations, and for carrying out control strategies for the monitored components.
This method allows two or more identical or substantially identical components of the same type to be monitored so that the state of health (SOH) for each respective component be maintained between common upper and lower limits required for achieving the common parameter. The upper limit is determined by the component or components having the relatively higher SOH values. Hence, if the SOH for one component falls below a predetermined lower limit, which limit can be set as a percentage or a number of percentage points relative to the component having the highest SOH or relative to an average SOH for two or more components having the highest SOH, then the component or components having higher SOH values are operated so that the SOH of all such electrical components are maintained between the upper and lower limits. Ideally, the predicted parameter of the component having the lowest SOH can be moved up to the predicted parameter of the component having the highest SOH. In this example, the higher of the predicted parameters is deemed to be the desired common value. If this is not achievable, then the SOH of the electrical components are maintained between the upper and lower limits to balance the parameters towards a common value between the highest and the lowest predicted parameters. This ensures that all identical or substantially identical components of the same type are worn or degraded at the same or substantially the same rate.
According to one example, the method involves determining a control strategy for each of the electrical components using a current derivative of the state of health for each of the at least two electrical components.
Alternatively, or in addition, the method involves calculating a predicted parameter relating to the life time or remaining operating time for each electrical component based on a current value of the derivative of the state of health for each electrical component. Subsequently, the two or more electrical components are controlled based on the determined control strategy to equalize the predicted remaining operating times of the electrical components. According to the method a control strategy is selected that reduces the loading on at least the electrical component having the shortest predicted remaining operating time. Consequently, the selected control strategy increases the loading on at least the electrical component having the longest predicted remaining operating time.
In this context, the predicted remaining operating time can be the remaining time to a functional state requiring repair or replacement of either component. Alternatively, the predicted remaining operating time is the remaining life time of the electrical components. In both cases, an operating state inhibiting the use of the components is detected.
The method according to the invention can be used for monitoring and controlling two or more identical or substantially identical traction battery packs or super-capacitors. Alternatively, the electrical components can be two or more traction motors each connected to an individual driven axle one or more pairs of traction wheel motors, each motor being connected to a wheel on a driven axle. For instance, if the components comprise electric traction motors then the central controller can monitor one or more of average power consumption, peak current, resistance measurements, rotor speed, temperature, magnetic field strength or motor fault data for each of the motors. If the components comprise high voltage battery packs then the central controller can monitor one or more of internal resistance, capacitance, state of charge for any or all of a set of battery cells battery pack, charging rate, temperature or peak power.
According to a further alternative, the electrical components can be two or more power electronics components for controlling the traction voltage, such as inverters, DC/DC converters, AC/DC converters, pre-charge circuit components, battery chargers, or similar.
The central controller can include a set of aging models for the respective component. In this context, the term “aging model” refers to any device or software approach which estimates or predicts the degradation or deterioration of a given component over time, e.g., curves, formulas, lookup tables, recorded in a memory in the central controller. The set of aging models can model historic maintenance or contain statistical data describing the past performance of substantially identical components. The central controller can use such models and/or detected data for calculating and monitoring the SOH of the respective components, in order to estimate the degradation rate and remaining useful life of the individual component.
The present invention also relates to a computer program comprising program code means for performing the above method steps for controlling electrical components in a vehicle traction voltage system when said program is run on a computer. The invention also relates to a computer readable medium carrying a computer program comprising program code means for performing the above method steps for controlling electrical components in a vehicle traction voltage system when said program product is run on a computer. Further, the invention relates to a control unit for controlling electrical components in a vehicle traction voltage system, the control unit being configured to perform the above method steps.
The present invention also relates to a computer program, computer program product and a storage medium for a computer all to be used with a computer for executing the method as described in any one of the above examples.
The present invention also relates to a vehicle comprising multiple traction voltage systems, and where a control unit is arranged to perform the steps of the method as described in one of the above examples.